1. Field of the Invention
The present invention relates to particulate matter to which a thermoplastic elastomer has been applied. For example, the present invention relates to particles optionally individually coated with a first set of one or more layers of thermosetting resin, on a proppant such as sand or ceramic, and contains a thermoplastic elastomer. The present invention also relates to methods for making and using this product as a proppant, gravel pack, foundry sand, or for dust control that is normally associated with the production and handling of particulate materials such as sand, ceramic, fertilizer, coal, or the like. The thermoplastic elastomer may assist is particle strengthening, dust suppression, fracture suppression and other aspects of performance enhancement.
2. Background Description
The term “proppant” is indicative of particulate material which is injected into fractures in subterranean formations surrounding oil wells, gas wells, water wells, and other similar bore holes to provide support to hold (prop) these fractures open and allow gas or liquid to flow through the fracture to the bore hole. Proppants are commonly used to prop open fractures formed in subterranean formations such as oil and natural gas wells during hydraulic fracturing.
One class of proppants contains particles lacking a resin coat. The uncoated proppants are typically particles of sand, ceramics, glass beads, walnut shells, or the like, as known in the art.
Another class of proppants includes coated proppants wherein individual particles are coated with a resin. The individual particles are typically particles of sand, ceramics, glass beads, walnut shells, or the like, as known in the art. The proppant coatings may be precured or curable. The precured proppants include a substrate core and a coating of resin cured prior to insertion into the subterranean formation. The curable proppants include a substrate core and a coating of resin cured downhole to form a consolidated proppant pack. Resin formulations typically used for curable coatings on proppant substrates (sand, ceramic, or the like) result in a highly crosslinked coating on the surface of the substrates.
Another class of proppants includes a homogeneous composite particle comprising fine particulate material bound by a binder wherein the binder comprises curable or precured resin. The composite particles have special and unique properties such as controlled plasticity and elasticity behavior. Because of these unique properties, the composite particles can be applied as the sole proppant in a 100% proppant pack (in the hydraulic fracture) or as a part replacement of existing commercial available ceramic and/or sand-based proppants, resin-coated and/or uncoated, or as blends between those. The composite particles can also be employed as the sole media in a 100% filtration pack or blended with other filtration media. Such composite particles are disclosed by U.S. Pat. No. 6,406,789 and U.S. patent application Ser. No. 09/450,588 and U.S. patent application Ser. No. 09/774,881, incorporated herein by reference in their entirety.
Curable resin coated proppants and precured resin coated proppants have been commercially available for use as propping agents. A curable proppant has a resin coating that includes a resin that is at least partially, and not fully, cured. In contrast, a “precured” proppant has a cured resin coating. The terms “cured” and “curable” are defined for the present specification by three tests historically employed in the art.
Temperature Stick Point Test: placing coated material on a heated melt point bar and determining the lowest temperature at which the coated material adheres to the melt point bar. A “sticking temperature” of greater than 350° F., typically indicates a cured material, depending upon the resin system used.
Acetone Extraction Test: an acetone extraction method, as described below, to dissolve the fraction of resin within the coating that is uncured.
Compressive Strength Test: no bonding, or no consolidation of the coated particles, following wet compression at 1000 psi at 200° F. for a period of as much as 24 hours, typically indicates a cured material.
However, unless otherwise indicated, the terms cured and curable are defined by the Acetone Extraction Test.
Another well completion system protects the well borewall production integrity by a tightly packed deposit of aggregate comprising sand, gravel or both between the borewall and the production pipe thereby avoiding the time and expense of setting a steel casing from the surface to the production zone which may be many thousands of feet below the surface. The gravel packing is inherently permeable to the desired hydrocarbon fluid and provides structural reinforcement to the borewall against an interior collapse or flow degradation. Such well completion systems are called “open hole” completions. The apparatus and process by which a packed deposit of gravel is placed between the borehole wall and the production pipe is encompassed within the definition of an “open hole gravel pack system.” Unfortunately, other commercially available open hole gravel pack systems for placing and packing gravel along a hydrocarbon production zone have been attended by a considerable risk of precipitating a borehole wall collapse due to fluctuations in the borehole pressure along the production zone. These pressure fluctuations are generated by surface manipulations of the downhole tools that are in direct fluid circulation within the well and completion string. Further discussion of gravel packs is presented by U.S. Pat. No. 6,382,319 incorporated herein by reference.
Moreover, sand control is another consideration when extracting hydrocarbons such as natural gas and crude oil from the earth's subsurface formations, from boreholes drilled into hydrocarbon bearing production zones. Production of oil, gas and water from unconsolidated or weakly consolidated formations is normally accompanied by the production of formation sand particles along with the produced fluids. The production of sand with the well fluids poses serious problems such as the erosion of sub-surface and surface production facilities and the accumulation of the sand in the wellbore and surface separators. Several methods such as gravel packing, screens and plastic consolidation have been in use for many years with varying success. However, these methods have several-technical and cost limitations. Further discussion of sand control is presented by U.S. Pat. No. 6,364,019 incorporated herein by reference in its entirety.
To maintain the productivity of a borehole and control the flow of hydrocarbon fluids from the borehole, numerous other devices and systems have been employed to prevent the natural forces from collapsing the borehole and obstructing or terminating fluid flow therefrom. One such system provides a full depth casement of the wellbore whereby the wellbore wall is lined with a steel casing pipe that is secured to the bore wall by an annulus of concrete between the outside surface of the casing pipe and the wellbore wall. The steel casing pipe and surrounding concrete annulus is thereafter perforated by ballistic or pyrotechnic devices along the production zone to allow the desired hydrocarbon fluids to flow from the producing formation into the casing pipe interior. Usually, the casing interior is sealed above and below the producing zone whereby a smaller diameter production pipe penetrates the upper seal to provide the hydrocarbon fluids a smooth and clean flowing conduit to the surface.
Although particles, whether proppants, gravel pack, or for sand control are very useful for improving the production of oil and gas from subterranean formations it would be desirable to increase yields of these particles during their manufacture by reducing fracturing into particles of any other sizes than the original targeted materials. The particles, for example dust, generated from mechanical abuse during manufacturing may reduce yield of particles of suitable size for use. The particles may also be associated with potential plugging that may occur within the formation and a subsequent reduction of the hydrocarbon production. For purposes of this description, dust is defined as dry solid particles less than about 300 microns (about 50 mesh) or less.
The dust or particles generated during transportation to the site of the subterranean formation, and handling at the site of the subterranean formation may also reduce the activity of coated particles available for use. Dust injected into or generated within the subterranean formation may also have detrimental effects.
Thus, it would be desirable to provide particles for use as proppants, gravel pack, and/or for sand/proppant control in subterranean formations with improved suppression of dust formation or fracture during their manufacture, transportation, or use as it is being handled at the subterranean formation both above ground (prior to injection into the formation) and downhole within the formation.
U.S. Pat. No. 4,732,920 to Graham et al., incorporated herein by reference, discloses a particulate material for use in treating subterranean formations as a proppant and/or as a fluid loss agent in hydraulic fracturing and as a screening material in gravel packing comprised of heat curable particles capable of forming a cohesive mass. The particles comprised of a high strength center, a coupling agent chemically bound to the center with a heat curable resin coated over the center. '920 to Graham asserts the incorporation of a small amount of polyvinyl acetal resin into the resin coating to increase the resin strength and thereby reduce its brittleness. '920 to Graham asserts this results in the virtual elimination of the dusting problem. The preferred polyvinyl acetal for '920 to Graham is polyvinyl butyral. Specifically '920 to Graham asserts a polyvinyl butyral, BUTVAR B-76, manufactured by Monsanto Co. strengthens the resin and eliminates the dust problem. (B-76 denotes a solid thermoplastic material that is offered at present by Solutia, not Monsanto.) Polyvinyl formals may also be used.
It would be desirable to increase the capacity of the particles to take an impact and not fracture. There is still a need for technology to reduce or eliminate dustiness and improve fracture resistance and strength of resin coated particles employed in subterranean formations.